1. Field of the Invention
The present invention relates to a fluid distribution system, and in particular a valve, which reduces the noise generated by a fluid flowing therethrough.
2. Description of the Related Art
When reducing the pressure of a fluid in a system, noise may typically be generated by a fluid distribution system, such as a valve. Depending upon the environment in which the valve is used, the generation of such noise may be harmful to those persons exposed to it in terms of possible damage to their hearing. The Occupational Safety and Health Administration (OSHA) has set the standard for the basic permissible noise intensity to which a person may be exposed for a duration of eight hours a day at 90 dBA. In addition, noise can have an adverse effect such as structural fatigue and/or equipment malfunction in the system in which the valve is utilized. Thus, in industrial applications, noise generation from pressure reduction is clearly undesirable.
Valves are a major source of industrial noise pollution due to the fact that they conduct fluids through orifices which restrict the flow thereof and cause unstable separation of flow. Noise can be classified as two types--broad band and narrow band, the latter including pure tones. Unacceptable noise levels in valves usually occur when pure tone excitation (whistle or screech) is involved. Whistle or screech is caused by the unstable separation of flow over a sharp edge or in the wake of a blunt body and coupling between this flow and acoustic modes within the surrounding cavities and pipe. This unstable flow separation, when stimulated by the acoustic modes of the chamber, can result in high intensity feedback oscillations and related emission of sound.
Reducing the noise generated by the fluid flowing through a valve has been accomplished by a variety of devices. In cage trim valves, in which a cage trim guides a valving element in its travel relative to a valve seat, the trim configuration has been a focus of noise-reducing efforts. The typical modification to the trim restricts the fluid flow rate through the trim, which reduces noise. The prior art shows many such modifications, for example, U.S. Pat. No. 3,954,124 to Self, which discloses nested concentric sleeves for subdividing the flow of fluid through a fluid control valve into a plurality of streams between the valve inlet and outlet. U.S. Pat. No. 4,384,592 to Ng discloses a cylindrical valve trim which has holes in the valve trim wall that pass through the wall at predetermined angles to create a plurality of counter-rotating vortices.
U.S. Pat. No. 4,860,993 to Goode incorporates a cage design using axially spaced sets of ports interconnected by plenums to direct multiple flow streams through a series of changes of direction to reduce the velocity and pressure of the fluid. U.S. Pat. No. 3,776,278 to Allen discloses a control valve including a perforated sleeve-like cage member, where fluid flow is directed through the perforations to partition the flow, thereby attenuating noise.
These devices of the prior art deal with reducing broad band noise generated at the outlet of the device. None of the devices of the prior art have dealt with the problem of reducing narrow band or pure tone noise generated at the inlet. In fact, in some cases, these devices may generate undesirable pure tones in the range of human hearing.
Moreover, these devices tend to become clogged by particulate matter entrained in the fluid because they incorporate a circuitous path design. For this reason, they are difficult to manufacture and maintain. Thus, the known prior art approaches to reducing valve noise increase the cost of manufacturing and maintenance and decrease the reliability of valves, while increasing the potential for valve failure.
Accordingly, it is an object of the present invention to provide an approach for eliminating narrow band or pure tone noise in a fluid distribution system, and specifically in a valve.
It is also an object of the present invention to provide a plate for a fluid distribution system and a sleeve for a valve which reduce the noise produced by fluid flowing through the system or the valve.
Yet another object of the present invention is to provide a fluid distribution system and a valve which incorporate a simple, straight flow path and which are thus easy and inexpensive to manufacture and maintain.
A further object of the present invention is to provide a sleeve which can be installed in existing valves with a minimum of disruption.
Another object of the present invention is to design a valve which reduces the noise produced by fluid flowing therethrough.
It is intended that the fluid distribution system of the present invention includes a variety of devices, such as valves, dryers, fluid impingement devices and flow restrictors.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.